1. Technical Field
The present invention relates to a flexible display substrate, and, more particularly, to a method of manufacturing a flexible display substrate having low moisture permeability and oxygen permeability, which can inhibit and prevent the shortening of the lifespan of organic devices attributable to extraneous moisture or oxygen.
2. Description of the Related Art
Liquid crystal displays (LCDs), in which a glass substrate is used as a substrate, were first developed early in the 1960's, and have been widely used in information display apparatuses, such as calculators, clocks, mobile phones, personal digital assistants (PDAs), audios, videos, computers, automobile instrument panels and the like. However, such LCDs, whose substrate is made of glass, are problematic although they are widely used.
The problems of these LCDs are caused by characteristics of the glass substrate which is used. That is, the LCDs are problematic in that the glass substrate which is used is fragile, heavy and inflexible and in that it is of limited thickness. In order to solve the above problems, it is required to replace a glass substrate with a plastic substrate.
Recently, with the advancement of display devices, it has been required that gas barrier films used in liquid crystal displays (LCDs) and organic light emitting diodes (OLEDs) be lighter and larger, and that the gas barrier films be easy to bend and fold such that they can be used in flexible displays.
Therefore, a transparent plastic substrate or a resin film-based substrate is being studied instead of a glass substrate which is heavy and fragile, and which is difficult to be used as a large area substrate. That is, it is required that the substrates used in liquid crystal displays (LCDs), organic light emitting diodes (OLEDs) displays or e-paper displays (EPDs) have high mechanical flexibility and excellent gas barrier properties.
However, the gas barrier properties of a plastic substrate or a resin film-based substrate are not better than those of a glass substrate, so that water vapor or oxygen permeates them. As a consequence, the lifespan and quality of liquid crystal displays (LCDs) or organic light emitting diodes (OLEDs) displays are deteriorated.
In order to solve such a problem, a film (transparent plastic substrate) having an excellent gas barrier property was fabricated by depositing a metal oxide film on top of the transparent plastic substrate. For example, a gas barrier film, which is fabricated by placing a silicon oxide film on a plastic film using vapor deposition, and a gas barrier film, on which an aluminum oxide film is formed, has been proposed.
Meanwhile, since the above-mentioned gas barrier films have a high water vapor transmission rate of 1 g/m2/day, which is measured by the Mocon method, there is a problem in that the water vapor barrier property of the above-mentioned gas barrier films is not satisfactory. In order to solve this problem, a moisture-proof film, which is formed by vapor-depositing at least one metal oxide selected from the group consisting of indium (In) oxide, tin (Sn) oxide, zinc (Zn) oxide and titanium (Ti) oxide on polyethylene terephthalate, has been proposed. However, this moisture-proof film is also problematic in that it does not satisfy the conditions for moisture permeability or mechanical flexibility.
The reason why a film (a flexible substrate) is required to have moisture-proof properties while high definition liquid crystal displays (LCDs) or organic light emitting diodes (OLEDs) displays are increasingly used is because, when water vapor or oxygen permeates into an organic light emitting diodes (OLEDs) display device, the organic light emitting diodes (OLEDs) display device is remarkably deteriorated by moisture existing in the interface between its cathode layer and organic layer, and dark spots where no light emits, occur. That is, extraneous moisture or oxygen degrades organic molecules, thus shortening the lifespan of the organic light emitting diodes (OLEDs) display device.